LOW-FREQUENCY DIELECTRIC PERMITTIVITY OF C-60

Complex dielectric response measurements have been made on a C-60/C-70 mixture pellet. The frequency and temperature ranges cover from 20 Hz to 1 MHz and from 30 to 300 K. Results show that the real part of the dielectric constant is 5 with a weak thermally activated polarization contribution. This thermal polarization is believed to be related to reorientation of C-60 molecules recently observed by many techniques such as NMR, sound velocity, thermal conductivity, and others. Our data yield relaxation frequencies for reorientation, indicating that the presence of an additional electric dipole moment of the orientationally ordered C-60 molecules at low temperature contributes 0.2-0.3 to the static dielectric constant.